The Hubble Space Telescope (HST) is a space-based telescope that was launched
in 1990 by the space shuttle. From its position 343 miles (552 km) above Earth’s
surface, the HST has expanded our understanding of star birth, star death,
and galaxy evolution, and has helped move black holes from theory to fact.
In its first 15 years, the telescope recorded over 700,000 images.

Hubble's view is so spectacular because of its location above Earth's atmosphere. Shifting pockets of air distort light from space  that's why stars seem to twinkle when viewed from the ground. Furthermore, the atmosphere blocks some wavelengths of light partially or entirely, making space the only place where it is possible to get a truly clear and comprehensive view of the universe.

These are not the only instruments that have flown aboard Hubble. The telescope was designed to be visited periodically by astronauts, who bring new instruments and technology, and make repairs. Perhaps the most famous of these servicing missions is the first, in 1993. After its 1990 launch, Hubble's primary mirror was discovered to be out of shape on
the edges by 1/50 of a human hair. This very small defect made it difficult
to focus faint objects being viewed by Hubble. Astronauts installed corrective optics on the telescope, fixing the flawed vision. Four more astronaut visits would follow, each boosting Hubble's observatory capabilities.

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